Is it possible to add spring/jiggle physics to a rigify metarig?
Didn't actually find an answer to my own question but did find a workaround, so I am posting in case it shows in search results.
Basically, while applying the addons to the bones in the metarig don't work as far as I see, you can apply it to the drivers in the generated rig and those do survive a regeneration of the rig.
I found that works best to apply it on rig types for single bones (like basic.super_copy or basic.raw_copy) or bone chains controlled in a FK fashion (like basic.copy_chain)